Wireless transmission device and wireless transmission method

Abstract

To suppress generation of interference of wireless signals even in a case where there is any other signal source than the own device that transmits a wireless signal in the same frequency band which causes interference.SOLUTION: A wireless transmission device comprises: an application unit that acquires a plurality of network packets configuring image data of an imaging area; a wireless unit that generates a wireless packet for wireless transmission from each of the plurality of network packets; and a transmission unit that transmits the wireless packet to a receiver via an antenna. The wireless unit at least has a wireless retransmission rate control unit that decides a communication rate for retransmitting the wireless packet, on the basis of the intensity of a reception signal from the receiver. The transmission unit retransmits the wireless packet by using the communication rate decided by the wireless retransmission rate control unit.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present disclosure relates to a wireless transmission device and a wireless transmission method.

Background Art

[0002] Patent Document 1 discloses a wireless LAN device that performs data communication using radio waves in a frequency band close to the microwave for heating generated by a microwave oven in the vicinity of the microwave oven. The wireless LAN device includes an electronic range operation detection device installed in the electronic range and including a detection circuit that detects the timing when microwaves are generated and a transmission circuit that transmits a signal representing the detection result of the detection circuit, and a plurality of wireless terminal devices that perform data communication using radio waves. Each wireless terminal device switches between a first data communication method for performing wireless communication when microwaves are not generated from the electronic range and a second data communication method that enables communication in a state with less interference by microwaves when microwaves are generated from the electronic range.

[0003] Patent Document 2 discloses a wireless LAN system formed by wirelessly connecting a base device and one or more terminal devices. The base device includes a receiving means for receiving channel change requests from terminal devices, a level detection means for detecting the level of the received signal of each available wireless channel when the device is started up, when a channel change request is received through the receiving means, or both, a signal discrimination means for determining whether the received signal being detected is a wireless LAN signal, and a QoS discrimination means for determining whether the wireless LAN signal is a QoS (Quality of Services) guaranteed signal when the signal discrimination means determines that it is a wireless LAN signal. The terminal device includes an error detection means for detecting demodulation errors that occur when a received signal is demodulated, an error amount discrimination means for determining whether the number of detected demodulation errors exceeds a predetermined threshold, a change request generation means for generating a channel change request when the error amount discrimination means determines that the number of detected demodulation errors exceeds the threshold, and a change request transmission means for transmitting the channel change request generated by the change request generation means to the base device. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-224176 [Patent Document 2] Japanese Patent Publication No. 2004-96595 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Patent Document 1 assumes that a microwave oven operation detection device is installed inside the microwave oven, enabling the wireless LAN device to recognize the timing of microwave emission from the microwave oven. Therefore, unless a microwave oven operation detection device is installed, the wireless LAN device cannot recognize the timing of microwave emission, leading to interference of wireless signals due to the use of the same frequency band, which increases the likelihood of data transmission errors. This is not limited to microwave ovens; similar problems are thought to occur in wireless LANs that transmit and receive wireless signals using the same frequency band as microwave ovens, as described in Patent Document 2. In other words, when handling wireless signals in a frequency band commonly used by microwave ovens and wireless LANs (e.g., the 2.4GHz band), if there is a signal source other than the device that emits wireless signals in the same frequency band (e.g., the 2.4GHz band) that causes interference, wireless signal interference will occur. Therefore, even if the microwave oven operation detection device configuration of Patent Document 1 cannot be installed, it is necessary to suppress the occurrence of interference with signal sources that emit wireless signals in the same frequency band (e.g., the 2.4GHz band).

[0006] This disclosure was devised in view of conventional circumstances and aims to provide a wireless transmission device and wireless transmission method that suppress the occurrence of wireless signal interference even when there is a signal source other than the device itself that transmits wireless signals in the same frequency band that cause interference. [Means for solving the problem]

[0007] This disclosure comprises an application unit that acquires a plurality of network packets constituting image data of an imaging area, a radio unit that generates a radio packet for radio transmission from each of the plurality of network packets, and a transmission unit that transmits the radio packet to a receiver via an antenna, wherein the radio unit has at least a radio retransmission rate control unit that determines a communication rate for retransmitting the radio packet based on the strength of the received signal from the receiver, and the transmission unit retransmits the radio packet using the communication rate determined by the radio retransmission rate control unit. The wireless retransmission rate control unit, when the strength of the received signal from the receiver is less than the retransmission rate threshold, selects a second correspondence table that defines the relationship between the communication rate, including the minimum retransmission rate for transmitting the wireless packet, and the number of retransmissions of the wireless packet. Based on the selected second correspondence table, the unit determines the communication rate for transmitting the wireless packet. The second correspondence table defines the relationship between the communication rate and the number of retransmissions of the wireless packet, such that the communication rate is discretely changed between the maximum and minimum communication rates and between the minimum and maximum communication rates when the number of retransmissions is from 1 to K (K: a default integer of 2 or more), the communication rate is gradually reduced toward the minimum communication rate when the number of retransmissions is from (K+1) to L (L: a default integer of (K+2) or more), and the communication rate is fixed and maintained at the minimum communication rate when the number of retransmissions is from (L+1) to M (M: a default integer of (L+2) or more). To provide a wireless transmission device.

[0008] Furthermore, this disclosure includes the steps of acquiring a plurality of network packets constituting image data of an imaging area, generating a wireless packet for wireless transmission from each of the plurality of network packets, and transmitting the wireless packet to a receiver via an antenna, wherein the step of generating the wireless packet further includes the step of determining a communication rate for retransmitting the wireless packet based on the strength of the received signal from the receiver, and the step of transmitting the wireless packet includes at least the step of retransmitting the wireless packet using the determined communication rate The step of generating the wireless packet further includes, if the strength of the received signal from the receiver is less than a retransmission rate threshold, selecting a second correspondence table that defines the relationship between the communication rate, including the minimum retransmission rate for transmitting the wireless packet, and the number of retransmissions of the wireless packet, and determining the communication rate for transmitting the wireless packet based on the selected second correspondence table, wherein the second correspondence table defines the relationship between the communication rate and the number of retransmissions of the wireless packet, wherein the communication rate is discretely changed between the maximum communication rate and the minimum communication rate and between the minimum communication rate and the maximum communication rate from 1 to K (K: a default integer of 2 or more), the communication rate is changed to gradually decrease toward the minimum communication rate from (K+1) to L (L: a default integer of (K+2) or more), and the communication rate is fixed and maintained at the minimum communication rate from (L+1) to M (M: a default integer of (L+2) or more). To provide a wireless transmission method. [Effects of the Invention]

[0009] According to this disclosure, even if there is a signal source other than the device that transmits wireless signals in the same frequency band that cause interference, the occurrence of wireless signal interference can be suppressed. [Brief explanation of the drawing]

[0010] [Figure 1] A diagram showing an example of the usage environment for the wireless transmission device related to this disclosure. [Figure 2] This figure shows an example of the characteristics of the signal strength over time of a wireless signal from a microwave oven. [Figure 3] This figure shows an example of the characteristics of the signal strength of a wireless signal from a wireless LAN router over time. [Figure 4] Block diagram showing a detailed internal configuration example of the camera according to this embodiment. [Figure 5] A diagram showing a list of set values ​​or thresholds. [Figure 6] A diagram showing a comparison of communication rates and various communication performance characteristics. [Figure 7] This diagram shows an example of a correspondence table for determining packet size and bandwidth according to the wireless environment. [Figure 8] A flowchart showing an example of a network packet generation procedure. [Figure 9]Flowchart showing an example of video communication quality evaluation procedure [Figure 10] Flowchart showing an example of video communication quality evaluation procedure [Figure 11] Flowchart showing an example of bandwidth control processing procedure [Figure 12] Flowchart showing an example of packet size processing procedure [Figure 13] Diagram showing an example of a correspondence table for determining an index of communication rate according to the number of retransmissions of wireless packets [Figure 14] Diagram showing an example of a correspondence table for determining an index of communication rate according to the number of retransmissions of wireless packets [Figure 15] Diagram showing an example of a table indicating the relationship between the number of retransmissions of wireless packets and the rate-down value of communication rate [Figure 16] Diagram showing an example of a table indicating the relationship between the number of retransmissions of wireless packets and the rate-down value of communication rate [Figure 17] Flowchart showing an example of retransmission rate processing procedure [Figure 18] Flowchart showing an example of retransmission rate processing procedure [Figure 19] Diagram showing a comparison of an example of the signal waveform of interference radio waves from a microwave oven and an example of the signal waveform of the network packet transmission signal of a camera [Figure 20] Diagram showing a comparison of an example of the signal waveform of interference radio waves from a wireless LAN repeater and an example of the signal waveform of the transmission signal of a wireless packet of a camera [Figure 21] Diagram showing a comparison of an example of the signal waveform of interference radio waves from a wireless LAN repeater and an example of the signal waveform of the transmission signal of a wireless packet of a camera [Figure 22] Diagram showing a comparison of an example of the signal waveform of interference radio waves from a wireless LAN repeater and an example of the signal waveform of the transmission signal of a wireless packet of a camera [[ID=4l]]

Mode for Carrying Out the Invention

[0011] The following describes in detail embodiments of the wireless transmission device and wireless transmission method disclosed herein, with appropriate reference to the attached drawings. However, unnecessary details may be omitted. For example, detailed explanations of already well-known matters and redundant explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding by those skilled in the art. The attached drawings and the following explanation are provided to enable those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter described in the claims.

[0012] Figure 1 shows an example of the usage environment of the wireless transmission device according to this disclosure. Hereinafter, the camera 100 will be used as an example to explain the wireless transmission device according to this disclosure. However, the wireless transmission device according to this disclosure is not limited to the camera 100, and for example, the intercom sub-unit IPT1, portable handsets HS1a and HS1b in Figure 1 may each be wireless transmission devices.

[0013] Recently, various network environments exist for transmitting and receiving data using wireless communication between numerous electronic devices. In this embodiment, we will explain using a wireless LAN (Local Area Network), also known as Wi-Fi®, which uses the 2.4GHz band that overlaps with the ISM (Industrial Scientific and Medical) band. As shown in Figure 1, Wi-Fi® is a wireless communication method that supports wireless communication between electronic devices via repeaters (routers) in each room of an apartment building or condominium where multiple rooms are built adjacent to each other. For example, Wi-Fi® can be used in the user's room RM1 of camera 100 (hereinafter simply abbreviated as "user") and in the neighbor's room RM2.

[0014] In the user's room RM1, the intercom master unit IPM1, located in the center of the living room, acts as the communication partner (and may also be referred to as the "receiver"). The intercom slave unit IPT1 at the entrance, the camera 100 that films the living room or balcony, and the portable handsets HS1a and HS1b can each communicate wirelessly with each other using the 2.4GHz band of Wi-Fi®. However, when using the 2.4GHz band, which overlaps with the ISM band, for Wi-Fi®, if radio waves (in other words, interference signals) are generated from electronic devices that use the ISM band frequency band (e.g., microwave oven MW1), interference occurs in Wi-Fi® communication, degrading the quality of wireless communication. This does not occur independently and limited to the user's room RM1 or the neighbor's room RM2, but can also occur if an ISM band interference source (e.g., microwave oven MW2) exists in the other room RM2 from the perspective of room RM1.

[0015] Furthermore, sources of interference to Wi-Fi® communication are not limited to ISM band devices (e.g., microwave ovens), but also include other Wi-Fi®-compatible electronic devices that use the same frequency band (i.e., the 2.4GHz band) (e.g., a Wi-Fi® compliant wireless LAN router RT1). For example, if your neighbor is using Wi-Fi® in another room RM2 for watching videos, downloading large amounts of data, playing online games for extended periods, interference may occur when you use Wi-Fi® in your own room RM1. Although not shown in Figure 1, interference in wireless communication when using the 2.4GHz band, which overlaps with the ISM band, for Wi-Fi® can occur not only in individual rooms of an apartment building but also on the premises of a private house. In particular, even within the premises of a private residence, if you try to use the 5GHz band between the outdoor area of ​​the residence (for example, an intercom sub-unit installed near an outdoor mailbox) and the indoor area (for example, an intercom master unit), it will overlap with the 5GHz band used for satellite detection and cannot be used. Therefore, it is necessary to use the 2.4GHz band Wi-Fi (registered trademark), which will result in interference from radio waves from microwave ovens and other devices.

[0016] Figure 2 shows an example of the characteristics of the signal strength over time of a wireless signal from a microwave oven. In the upper part of Figure 2, the horizontal axis represents time, and the vertical axis conceptually represents the signal strength (signal level). The lower part of Figure 2 shows an example of the signal waveform during the ON period (see below).

[0017] For example, in western Japan, microwave ovens operate by repeatedly switching on and off at a predetermined duty cycle with a period of 8.33 ms. In eastern Japan, microwave ovens operate by repeatedly switching on and off at a predetermined duty cycle with a period of 10 ms. For example, as shown in Figure 2, a microwave oven operates with a duty cycle of 8.33 ms, with an on period of 6-7 ms and an off period of 1.33-2.33 ms. In other words, the off period is shorter than the on period. Note that the duty cycle may vary depending on the specifications of the microwave oven; if the on period is 6 ms, the off period is 2.33 ms, and if the on period is 7 ms, the off period is 1.33 ms. During the on period, the microwave oven emits strong radio waves (interfering radio waves) of approximately -4 dBm and -12 dBm, as shown in characteristics MVPY1a and MVPY1b, respectively. The intensity of these interfering radio waves is about the same as the intensity of radio waves transmitted by, for example, a wireless LAN router. Therefore, attempting to transmit the desired Wi-Fi® wireless signal (wireless packet) in the ON section will result in wireless communication interference. In other words, the interference from the microwave oven will prevent the transmission of the desired Wi-Fi® wireless signal.

[0018] Figure 3 shows an example of the characteristics of the signal strength of a wireless signal from a wireless LAN router over time. In Figure 3, the horizontal axis represents time, and the vertical axis conceptually represents the signal strength. Unlike a microwave oven, the strength (signal level) of radio waves (interference signals) emitted from a wireless LAN router fluctuates irregularly over time and is characterized by moment-to-moment changes depending on the wireless environment, including the usage pattern of the wireless LAN.

[0019] The signal strength characteristics shown in Figure 3 are just one example, but for instance, a 3.3ms on-interval with high signal strength (in other words, emitting strong interference) and a 0.7ms off-interval, a 12ms on-interval with moderate signal strength (in other words, emitting moderate interference) and a 1.0ms off-interval, a 0.5ms on-interval with low signal strength (in other words, emitting weak interference) and a 4.5ms off-interval, and a 0.5ms on-interval with extra-high signal strength (in other words, emitting extremely strong interference) are all examples of how signal strength fluctuates over time. Unlike microwave ovens, periodicity is not observed, but similarly, attempting to transmit a desired Wi-Fi® wireless signal (wireless packet) during an on-interval will result in wireless communication interference. In other words, interference from other wireless LAN routers will prevent the transmission of the desired Wi-Fi® wireless signal. In this context, "the user's own device" refers to a wireless transmitting device that communicates wirelessly with a communication partner (for example, the intercom master unit IPM1, see Figure 1) using the 2.4GHz band of Wi-Fi (registered trademark), such as the camera 100 described later.

[0020] Figure 4 is a block diagram showing a detailed internal configuration example of the camera 100 according to this embodiment. The camera 100 includes an application unit 1, a wireless unit 2, and a transmitting / receiving unit 3. The application unit 1 includes a camera unit 11, a packet size control unit 12, a network packet generation unit 13, a video communication quality evaluation unit 14, and a bandwidth control unit 15. The wireless unit 2 includes a wireless buffer 21, a wireless packet generation unit 22, a wireless transmission control unit 23, a wireless retransmission rate control unit 24, a wireless retransmission control unit 25, a wireless reception control unit 26, a wireless reception field strength measurement unit 27, and a wireless communication quality evaluation unit 28. The transmitting / receiving unit 3 includes an RF (Radio Frequency) unit 31, an amplifier unit 32, and an antenna 33.

[0021] The following describes the various parts of Camera 100.

[0022] The application unit 1 acquires multiple network packets that constitute the image data of the imaging area. The imaging area is, for example, the living room or balcony of the user's room RM1 (see Figure 1), but it may be any other area depending on the orientation of the camera 100. The packet size control unit 12, the network packet generation unit 13, the video communication quality evaluation unit 14, and the bandwidth control unit 15 are each composed of a processor such as a CPU (Central Proceeding Unit) or FPGA (Field Programmable Gate Array) and memory such as RAM (Random Access Memory) and ROM (Read Only Memory), and the functions of each unit are realized by these components.

[0023] The camera unit 11 includes at least a lens and an image sensor, and generates image data of the imaging area (see above) by imaging a subject (e.g., the user, the user's family, the user's pet; the same applies hereinafter) within the imaging area. The lens includes, for example, a focus lens and a zoom lens. Incident light, which is light reflected by the subject, enters the lens. The light formed by the lens enters the light-receiving surface (imaging surface) of the image sensor as an optical image of the subject. Depending on the installation location of the camera 100 or the shooting application, lenses with various focal lengths or shooting ranges can be used. The image sensor includes a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor with multiple pixels arranged to be suitable for imaging visible light or near-infrared light, and a signal processing circuit (not shown). The image sensor performs photoelectric conversion, which converts the light (optical image of the subject) incident on the light-receiving surface (imaging surface) composed of multiple pixels into an electrical signal. The image sensor acquires electrical signals of either RGB (Red, Green, Blue) color images or monochrome images consisting of black and white luminance component signals, depending on the light reflected by the subject. The signal processing circuit of the image sensor (not shown) converts the electrical signals (analog signals) into digital image data and sends them to the packet size control unit 12 based on instructions from the bandwidth control unit 15 (for example, a bandwidth specification instruction that specifies the bandwidth that defines the amount of data per frame of the image data). In other words, the signal processing circuit of the image sensor (not shown) generates image data with a defined amount of data per frame (in other words, resolution) in response to the bandwidth specification instruction from the bandwidth control unit 15 and sends it to the packet size control unit 12.

[0024] The packet size control unit 12 generates multiple data packets by dividing the image data from the camera unit 11 based on instructions from the video communication quality evaluation unit 14 (for example, a size change instruction or a size maintenance instruction), and sends them to the network packet generation unit 13. The size instructed by the video communication quality evaluation unit 14 is the size of the image data stored in one data packet, and there are six types, as shown in Figure 7 (see below). The smallest size (1) is 64 bytes, the next largest size (2) is 128 bytes, the next largest size (3) is 256 bytes, the next largest size (4) is 512 bytes, the next largest size (5) is 1.0k bytes, and the largest size (6) is 1.5k bytes. Note that these byte counts are just examples. The detailed operation procedure of the packet size control unit 12 will be described later with reference to Figure 12.

[0025] The network packet generation unit 13 generates network packets by adding various predetermined headers (e.g., RTP (Realtime Transport Protocol) header, UDP (User Datagram Protocol) / IP (Internet Protocol) header) to individual data packets from the packet size control unit 12. The network packet generation unit 13 writes each generated network packet to the wireless buffer 21. The network packet generation unit 13 also sends parameters related to writing network packets to the wireless buffer 21 (e.g., the number of discarded packets Y, the total amount of data successfully written to the wireless buffer 21 per unit time D1) to the video communication quality evaluation unit 14. The detailed operation procedure of the network packet generation unit 13 will be described later with reference to Figure 8.

[0026] The video communication quality evaluation unit 14 periodically performs video communication quality evaluation processing to determine whether to maintain or change the bandwidth and packet size of the current image data, based on feedback from the wireless unit 2 (for example, the wireless quality evaluation result from the wireless communication quality evaluation unit 28). If the video communication quality evaluation unit 14 determines, for example, that the wireless quality evaluation result is "normal" and that both the bandwidth and packet size of the current image data should be maintained, it generates a bandwidth maintenance instruction and sends it to the bandwidth control unit 15, and generates a size maintenance instruction and sends it to the packet size control unit 12. On the other hand, if the video communication quality evaluation unit 14 determines, for example, that the wireless quality evaluation result is "good" or "bad" and that both the bandwidth and packet size of the current image data should be changed in conjunction, it determines the amount of change for each, generates a bandwidth change instruction including the amount of change for the bandwidth and sends it to the bandwidth control unit 15, and generates a size change instruction including the amount of change for the packet size and sends it to the packet size control unit 12. The detailed operation procedure of the video communication quality evaluation unit 14 will be described later with reference to Figures 9 and 10.

[0027] The bandwidth control unit 15 determines the bandwidth of the data packets generated by the camera unit 11 (i.e., the amount of data per frame, which can be considered as resolution) based on instructions from the video communication quality evaluation unit 14 (for example, a bandwidth change instruction or a bandwidth maintenance instruction). The bandwidth control unit 15 generates a bandwidth specification instruction specifying the determined bandwidth and sends it to the camera unit 11. The bandwidth instructed by the video communication quality evaluation unit 14 is the amount of data that constitutes the image per frame, and there are six types, as shown in Figure 7 (see below). The smallest bandwidth (1) is 128k bits (=16k bytes), the next largest bandwidth (2) is 256k bits (=32k bytes), the next largest bandwidth (3) is 512k bits (=64k bytes), the next largest bandwidth (4) is 1M bits (=125k bytes), the next largest bandwidth (5) is 2M bits (=250k bytes), and the largest bandwidth (6) is 4M bits (=500k bytes). Note that these bit counts are just examples. The detailed operating procedure of the bandwidth control unit 15 will be described later with reference to Figure 7 or Figure 11.

[0028] The wireless unit 2 generates wireless packets for wireless transmission from each of multiple network packets. The wireless packet generation unit 22, wireless transmission control unit 23, wireless retransmission rate control unit 24, wireless retransmission control unit 25, wireless reception control unit 26, wireless reception field strength measurement unit 27, and wireless communication quality evaluation unit 28 are each composed of a processor such as a CPU or FPGA and memory such as RAM and ROM, and the functions of each unit are realized.

[0029] The wireless buffer 21 is a memory such as RAM with a predetermined data capacity, and temporarily stores individual network packets generated by the network packet generation unit 13. The data size that can be written to the wireless buffer 21 is limited according to the memory specifications, and it is not possible to write network packets with a data size exceeding this limit.

[0030] The wireless packet generation unit 22 reads and acquires older network packets stored in the wireless buffer 21 in order, and generates wireless packets by adding various default headers for wireless transmission (e.g., MAC (Media Access Control) header, PHY (Physical: Physical Layer) header) to the read network packets. The wireless packet generation unit 22 sends each generated wireless packet to the wireless transmission control unit 23.

[0031] The wireless transmission control unit 23 sets a communication rate that indicates the communication speed when transmitting wireless packets from the wireless packet generation unit 22. The wireless transmission control unit 23 generates a baseband wireless signal by applying baseband processing such as modulation corresponding to the Wi-Fi® communication method to the wireless packet so that it transmits wirelessly at the set communication rate, and sends it to the RF unit 31. The wireless transmission control unit 23 also sets the wireless transmission control unit 23 to use the modified communication rate determined by the wireless retransmission rate control unit 24 when, for example, the wireless quality between the camera 100 and the receiver deteriorates or improves. Here, deterioration of wireless quality between the camera 100 and the receiver refers to cases where, for example, the received signal (e.g., the received response (Ack) corresponding to the wireless packet) is not received for a certain period of time. Improvement of wireless quality between the camera 100 and the receiver refers to cases where, for example, the strength of the received signal (e.g., the received response (Ack) corresponding to the wireless packet) is greater than a predetermined threshold (the retransmission rate electric field strength threshold TH_RSSI_FBLim, described later). Furthermore, the received signal is not limited to the received acknowledgment (Ack) corresponding to the wireless packet; for example, it may also be a wireless packet for wireless communication sent from the camera 100's communication partner (e.g., the intercom master unit IPM1 or a Wi-Fi® router not shown), and the same applies in the following explanation.

[0032] The wireless retransmission rate control unit 24 performs retransmission rate processing to dynamically change the communication rate when transmitting wireless packets based on the number of retransmissions and the received field strength of the received acknowledgment (Ack), in response to instructions from the wireless retransmission control unit 25 when the wireless quality between the camera 100 and the receiver deteriorates or improves. Note that the received field strength may be the received field strength of the wireless packets for wireless communication sent from the communication partner of the camera 100 (e.g., the intercom master unit IPM1 or a Wi-Fi® router not shown), and the same applies in the following description. The detailed operation procedure of the wireless retransmission rate control unit 24 will be described later with reference to Figures 17 and 18.

[0033] The wireless retransmission control unit 25, in response to an instruction from the wireless reception control unit 26 to retransmit a wireless packet when no received signal (e.g., an acknowledgment (Ack)) is received from the receiver for a certain period of time, generates an instruction to perform retransmission rate processing to determine the communication rate when transmitting the wireless packet and sends it to the wireless retransmission rate control unit 24. The wireless retransmission control unit 25 may also manage (keep) the total number of wireless packet retransmissions, in which case it may send the total number of retransmissions to the wireless communication quality evaluation unit 28.

[0034] The wireless reception control unit 26 receives the baseband band received signal from the RF unit 31. When the wireless reception control unit 26 does not receive a received signal (e.g., an acknowledgment (Ack)) from the receiver for a certain period of time, it generates an instruction to retransmit the wireless packet and sends it to the wireless retransmission control unit 25. The wireless reception control unit 26 also generates an instruction to measure the received field strength of the baseband band received signal (e.g., an acknowledgment (Ack)) sent from the RF unit 31 when the received signal (e.g., an acknowledgment (Ack)) from the receiver is received by the transmitting / receiving unit 3 and sends it to the wireless received field strength measurement unit 27.

[0035] The wireless reception field strength measurement unit 27 measures the received field strength of the received signal from the receiver (e.g., the received response (Ack) of a wireless packet) received by the transmitting / receiving unit 3 in response to instructions from the wireless reception control unit 26, and sends the measurement result (e.g., the received field strength RSSI_VI of the received response of a wireless packet) to the wireless communication quality evaluation unit 28.

[0036] The wireless communication quality evaluation unit 28 evaluates the quality of the wireless communication between the camera 100 and the receiver (e.g., "good", "average", "bad") based on the measurement result of the received field strength of the received signal (e.g., received response (Ack)) from the wireless received field strength measurement unit 27 and a predetermined threshold. The wireless communication quality evaluation unit 28 sends the evaluation result of the wireless communication quality to the video communication quality evaluation unit 14. If the wireless communication quality evaluation unit 28 evaluates the wireless communication quality between the camera 100 and the receiver as "good" or "bad", it may also generate an instruction to change the communication rate of the wireless packets and send it to the wireless retransmission rate control unit 24. In this case, the wireless retransmission rate control unit 24 may perform retransmission rate processing (see Figures 17 and 18) based on the instruction from the wireless communication quality evaluation unit 28.

[0037] The transmitting / receiving unit 3 transmits wireless packets generated by the wireless unit 2 to the receiver via the antenna 33. The transmitting / receiving unit 3 receives signals transmitted from the receiver or signals from signal sources other than the receiver via the antenna 33. The receiver is the communication partner of the camera 100 located in the user's room RM1, and is, for example, the intercom master unit IPM1, but may also be other electronic devices (for example, a Wi-Fi® wireless LAN router not shown). The signals transmitted from the receiver are the received responses (Ack: Acknowledgment) corresponding to wireless packets (for example, video captured by the camera 100). Similarly, signals from signal sources other than the receiver include interfering radio waves from a microwave oven or other wireless LAN routers, and wireless packets being communicated by other electronic devices.

[0038] The RF unit 31 upconverts the baseband radio signal from the wireless transmission control unit 23 to a 2.4GHz high-frequency signal and sends it to the amplifier unit 32. The RF unit 31 downconverts the high-frequency signal (for example, a 2.4GHz signal) received by the antenna 33 and amplified by the amplifier unit 32 to a baseband received signal and sends it to the wireless reception control unit 26.

[0039] The amplifier unit 32 amplifies the level of the 2.4GHz high-frequency signal from the RF unit 31 to a predetermined transmission power level for wireless transmission and sends it to the antenna 33. The amplifier unit 32 also amplifies the level of the high-frequency signal (for example, a 2.4GHz signal) received by the antenna 33 to a predetermined reception power level for wireless reception and sends it to the RF unit 31.

[0040] Antenna 33 transmits a 2.4GHz high-frequency signal amplified by amplifier 32 (i.e., radiates radio waves in the 2.4GHz band). Antenna 33 receives signals transmitted from the receiver or signals transmitted from sources other than the receiver. The signals received by antenna 33 are input to amplifier 32.

[0041] Figure 5 is a diagram showing a list of setting values ​​or thresholds. The setting values ​​or thresholds shown in Figure 5 are stored in the processor or memory of the corresponding component among the various parts of the camera 100 (see Figure 4).

[0042] The write wait time TW indicates a certain period of time during which writing to the wireless buffer 21 is delayed until the number of write retries N for network packets to the wireless buffer 21 reaches the upper limit value TH_N. The write wait time TW is managed (maintained) by the network packet generation unit 13, but may be referenced by other units.

[0043] The write retry count N indicates the number of write retries that are incremented when writing a network packet to the wireless buffer 21 fails. The write retry count N is managed (maintained) by the network packet generation unit 13, but may be referenced by other units.

[0044] The write retry limit value TH_N indicates the upper limit of the number of write retries N for network packets to the wireless buffer 21. The write retry limit value TH_N is managed (maintained) by the network packet generation unit 13, but may be referenced by other units.

[0045] The number of discarded packets Y indicates the number of network packets that are discarded due to timeout when the writing of network packets to the wireless buffer 21 fails, and the system waits for a certain period of time before writing to the wireless buffer 21, but the number of write retry counts N exceeds the upper limit value TH_N. The number of discarded packets Y is managed (maintained) by the network packet generation unit 13, but may be referenced by other units.

[0046] The quality judgment threshold TH_Y, based on the number of discarded packets, is a threshold referenced to determine the quality of wireless communication between the camera 100 and the receiver by comparing it with the number of discarded packets Y. The quality judgment threshold TH_Y, based on the number of discarded packets, is managed (maintained) by the video communication quality evaluation unit 14, but may also be referenced by other units.

[0047] The discarded packet / wireless bandwidth quality judgment threshold TH_OK_W is a threshold referenced to determine whether the writing of network packets to the wireless buffer 21 per unit time is successful or not, based on the current wireless bandwidth (bandwidth) settings. The discarded packet / wireless bandwidth quality judgment threshold TH_OK_W is managed (maintained) by the video communication quality evaluation unit 14, but may be referenced by other units.

[0048] The quality judgment threshold TH_W based on the successful wireless buffer write bandwidth is a threshold referenced to determine whether to increase or decrease the bandwidth from the current wireless bandwidth setting depending on the current wireless quality between the camera 100 and the receiver. The quality judgment threshold TH_W based on the successful wireless buffer write bandwidth is managed (maintained) by the video communication quality evaluation unit 14, but may be referenced by other units.

[0049] The current continuous wireless band good count OK_W indicates the number of times the current wireless band (bandwidth) setting, which affects the current wireless quality between the camera 100 and the receiver, has been evaluated by the wireless communication quality evaluation unit 28 as suitable (in other words, should be maintained). The current continuous wireless band good count OK_W is managed (maintained) by the video communication quality evaluation unit 14, but may be referenced by other units.

[0050] The retransmission rate field strength threshold TH_RSSI_FBLim is a threshold referenced to determine whether the received signal (e.g., an acknowledgment) from the receiver received by the camera 100 is in a weak field (i.e., the current wireless quality between the camera 100 and the receiver is poor). The retransmission rate field strength threshold TH_RSSI_FBLim is managed (held) by the wireless retransmission rate control unit 24, but may be referenced by other units.

[0051] The maximum number of retransmissions TH_RTYMAX is the maximum number of retransmissions allowed for a single wireless packet and is a default value (for example, "32" in the examples in Figures 13 and 14). The maximum number of retransmissions TH_RTYMAX is managed (maintained) by the wireless retransmission rate control unit 24, but may be referenced by other units.

[0052] The retransmission count T_RTY of a currently transmitted wireless packet indicates the number of times the camera 100 has retransmitted a wireless packet when the receiver has not received an acknowledgment (Ack) for that packet. The retransmission count T_RTY of a currently transmitted wireless packet is managed (maintained) by the wireless retransmission rate control unit 24, but may be referenced by other units.

[0053] The minimum retransmission rate FB_MIN indicates the minimum communication rate when transmitting a wireless packet. The minimum retransmission rate FB_MIN is set differently depending on the comparison result between the received field strength RSSI_VI of the wireless packet's received response (Ack) and the retransmission rate field strength threshold TH_RSSI_FBLim. The minimum retransmission rate FB_MIN is managed (maintained) by the wireless retransmission rate control unit 24, but may be referenced by other parts.

[0054] The RSSI_VI of the received field strength for the received response of a wireless packet indicates the received field strength measured by the wireless received field strength measurement unit 27 when the camera 100 receives a received response (Ack) based on the fact that a wireless packet from the camera 100 has been received by the receiver. The RSSI_VI of the received field strength for the received response of a wireless packet is managed (held) by the wireless received field strength measurement unit 27, but may be referenced by other units (for example, the wireless retransmission rate control unit 24).

[0055] The rate down value FB_DOWN(T_RTY) indicates a value that specifies how much the communication rate should be reduced from the current communication rate for transmitting wireless packets during the retransmission rate processing by the wireless retransmission rate control unit 24. The rate down value FB_DOWN(T_RTY) is managed (maintained) by the wireless retransmission rate control unit 24, but may be referenced by other units.

[0056] The bandwidth W_CAL, which represents the amount of network packets successfully written to the wireless buffer 21 per unit time, is calculated by dividing the total data amount D1 of network packets successfully written to the wireless buffer 21 per unit time by the time difference (for example, the difference between the time T1 when the previous video communication quality evaluation process was performed and the current time T2). The bandwidth W_CAL, which represents the amount of network packets successfully written to the wireless buffer 21 per unit time, is managed (maintained) by the wireless retransmission rate control unit 24, but may also be referenced by other units.

[0057] Figure 6 is a diagram showing a comparison of communication rates and various communication performance characteristics. In Figure 6, "index" is an identification number that identifies the communication rate when transmitting a wireless packet. In other words, in camera 100, the wireless retransmission rate control unit 24 identifies the communication rate when retransmitting a wireless packet using the index (identification number). Note that the wireless retransmission rate control unit 24 may use elements other than the index (identification number) to identify the communication rate.

[0058] In the example in Figure 6, under the IEEE (Institute of Electrical and Electronics Engineers) 802.11b communication standard, the maximum communication rate index is 2 (5.5 Mbps), and the minimum communication rate index is 0 (1 Mbps). Under the IEEE 802.11g communication standard, the maximum communication rate index is 10 (54 Mbps), and the minimum communication rate index is 3 (6 Mbps).

[0059] In the IEEE 802.11n, 11ac, and 11ax communication standards, the maximum communication rate index is 10 (i.e., MCS (Modulation and Coding Scheme) is 7), and the minimum communication rate index is 3 (i.e., MCS is 0). MCS is an index that defines the combination of modulation scheme and coding rate parameters in wireless communication in a stepwise manner. In particular, for IEEE 802.11n and 11ac, the maximum communication rate can be one of 65Mbps, 72.2Mbps, 135Mbps, or 150Mbps, and the minimum communication rate can be one of 6.5Mbps, 7.2Mbps, 13.5Mbps, or 15Mbps.

[0060] Furthermore, the larger the index, the shorter the range in wireless communication tends to be, the worse the reception sensitivity tends to be, the weaker the interference resistance tends to be, a higher communication bandwidth is more suitable, the lower the probability of interference and collisions tends to be, the shorter the packet length (i.e., the length of the data storage area within the packet) tends to be, and the shorter the transmission time tends to be.

[0061] On the other hand, the smaller the index, the easier it is to achieve a longer range in wireless communication, the better the reception sensitivity in wireless communication, the stronger the resistance to interference in wireless communication, the more suitable a lower communication bandwidth is for wireless communication, the higher the probability of interference and collisions in wireless communication, the longer the packet length (i.e., the length of the data storage area within the packet) in wireless communication, and the longer the transmission time in wireless communication tends to be.

[0062] Therefore, in this embodiment, in view of the relationship between the characteristics of interference resistance and interference collision probability in wireless communication and the communication rate, the wireless retransmission rate control unit 24 sets the communication rate based on the basic idea that when the wireless quality between the camera 100 and the receiver is good, the communication rate is set high (i.e., the index is set high), and when the wireless quality is poor, the communication rate is set low (i.e., the index is set low). In other words, even in an environment where there are microwave ovens or other wireless LAN routers that emit interfering radio waves in the same frequency band as the 2.4GHz band used by the camera 100, setting the communication rate index high enables wireless communication with a low interference collision probability, while setting the communication rate index low enables wireless communication with strong interference resistance. Furthermore, the wireless retransmission rate control unit 24 can flexibly set the communication rate according to the number of retransmissions based not only on the basic idea described above, but also on various correspondence tables shown in Figures 13 and 14. Details of setting the communication rate will be described later with reference to Figures 17 and 18.

[0063] Figure 7 shows an example of a correspondence table TBL1 for determining packet size and bandwidth according to the wireless environment. The wireless environment here refers to, for example, the wireless quality between the camera 100 and the receiver, and corresponds to the evaluation result by the wireless communication quality evaluation unit 28. The correspondence table TBL1 in Figure 7 may be stored, for example, in the memory (not shown) of the video communication quality evaluation unit 14. The correspondence table TBL1 defines six levels each for bandwidth and packet size, and defines the number of network packets required to form one image data according to each of the bandwidth and packet size. The larger the bandwidth and packet size, the higher the image quality of a single image data, resulting in a clearer image. On the other hand, the smaller the bandwidth and packet size, the lower the image quality of a single image data, resulting in a coarser image.

[0064] In this embodiment, the video communication quality evaluation unit 14 performs video communication quality evaluation processing (see Figures 9 and 10) to determine whether it is necessary to change the current image data bandwidth and packet size settings based on feedback from the wireless unit 2 (for example, the wireless quality evaluation result from the wireless communication quality evaluation unit 28). When the wireless quality between the camera 100 and the receiver deteriorates, the video communication quality evaluation unit 14 changes the bandwidth and packet size one step at a time without significantly changing the number of network packets required to form one image data image.

[0065] More specifically, if the current bandwidth is "bandwidth (6)" and the current packet size is "size (6)", and the wireless quality between the camera 100 and the receiver deteriorates, the video communication quality evaluation unit 14 generates a bandwidth change instruction to "bandwidth (5)" and a size change instruction to "size (5)". In this case, the video communication quality evaluation unit 14 sends an instruction to the network packet generation unit 13 to reduce the number of network packets required to form one image data from "333" to "250". In response to the instruction from the video communication quality evaluation unit 14, the network packet generation unit 13 generates "250" network packets to form one image data. In this example, we explained a case where the bandwidth and size are reduced by one step from "bandwidth (6)" and "size (6)" to "bandwidth (5)" and "size (5)". However, if the wireless quality between camera 100 and receiver improves, the bandwidth and size can be increased by one step from "bandwidth (5)" and "size (5)" to "bandwidth (6)" and "size (6)".

[0066] Furthermore, if the current bandwidth is "bandwidth(5)" and the current packet size is "size(5)", and the wireless quality between the camera 100 and the receiver deteriorates, the video communication quality evaluation unit 14 generates a bandwidth change instruction to "bandwidth(4)" and a size change instruction to "size(4)". In this case, the video communication quality evaluation unit 14 sends an instruction to the network packet generation unit 13 to reduce the number of network packets required to form one image data from "250" to "244". The network packet generation unit 13 generates "244" network packets to form one image data in response to the instruction from the video communication quality evaluation unit 14. In this example, we have described an example of a one-step decrease from "bandwidth(5)" and "size(5)" to "bandwidth(4)" and "size(4)", but similarly, if the wireless quality between the camera 100 and the receiver improves, it is possible to increase by one step from "bandwidth(4)" and "size(4)" to "bandwidth(5)" and "size(5)".

[0067] Similarly, if the current bandwidth is "bandwidth(4)" and the current packet size is "size(4)", and the wireless quality between the camera 100 and the receiver deteriorates, the video communication quality evaluation unit 14 generates a bandwidth change instruction to "bandwidth(3)" and a size change instruction to "size(3)". In this case, the video communication quality evaluation unit 14 sends an instruction to the network packet generation unit 13 to increase the number of network packets required to form one image data from "244" to "250". The network packet generation unit 13 generates "250" network packets to form one image data in response to the instruction from the video communication quality evaluation unit 14. In this example, we have described an example where the bandwidth decreases by one step from "bandwidth(4)" and "size(4)" to "bandwidth(3)" and "size(3)", but if the wireless quality between the camera 100 and the receiver improves, the bandwidth increases by one step from "bandwidth(3)" and "size(3)" to "bandwidth(4)" and "size(4)".

[0068] Similarly, if the current bandwidth is "bandwidth (3)" and the current packet size is "size (3)", and the wireless quality between the camera 100 and the receiver deteriorates, the video communication quality evaluation unit 14 generates a bandwidth change instruction to "bandwidth (2)" and a size change instruction to "size (2)". In this case, the video communication quality evaluation unit 14 sends an instruction to the network packet generation unit 13 to not change the number of network packets required to form one image data from "250". The network packet generation unit 13 generates "250" network packets to form one image data in response to the instruction from the video communication quality evaluation unit 14. In this example, we have described an example where the bandwidth decreases by one step from "bandwidth (3)" and "size (3)" to "bandwidth (2)" and "size (2)", but if the wireless quality between the camera 100 and the receiver improves, the bandwidth increases by one step from "bandwidth (2)" and "size (2)" to "bandwidth (3)" and "size (3)".

[0069] Similarly, if the current bandwidth is "bandwidth (2)" and the current packet size is "size (2)", and the wireless quality between the camera 100 and the receiver deteriorates, the video communication quality evaluation unit 14 generates a bandwidth change instruction to "bandwidth (1)" and a size change instruction to "size (1)". In this case, the video communication quality evaluation unit 14 sends an instruction to the network packet generation unit 13 to not change the number of network packets required to form one image data from "250". The network packet generation unit 13 generates "250" network packets to form one image data in response to the instruction from the video communication quality evaluation unit 14. In this example, we have described an example where the bandwidth decreases by one step from "bandwidth (2)" and "size (2)" to "bandwidth (1)" and "size (1)", but similarly, if the wireless quality between the camera 100 and the receiver improves, the bandwidth increases by one step from "bandwidth (1)" and "size (1)" to "bandwidth (2)" and "size (2)".

[0070] Similarly, if the current bandwidth is "bandwidth (1)" and the current packet size is "size (1)", and the wireless quality between the camera 100 and the receiver improves, the video communication quality evaluation unit 14 generates a bandwidth change instruction to "bandwidth (2)" and a size change instruction to "size (2)". In this case, the video communication quality evaluation unit 14 sends an instruction to the network packet generation unit 13 to not change the number of network packets required to form one image data from "250". The network packet generation unit 13 generates "250" network packets to form one image data in response to the instruction from the video communication quality evaluation unit 14.

[0071] Next, we will describe various examples of operation procedures for the camera 100 according to this embodiment.

[0072] Figure 8 is a flowchart showing an example of a network packet generation procedure. The network packet generation procedure shown in Figure 8 is mainly performed by the network packet generation unit 13.

[0073] In Figure 8, the network packet generation unit 13 reads and acquires various setting values ​​(step St1). These setting values ​​include, for example, the write wait time TW, the number of write retries N, the upper limit of the number of write retries TH_N, and the number of discarded packets Y. At step St1, the number of write retries N is 0 (zero). The network packet generation unit 13 acquires individual data packets that form an image from the packet size control unit 12 (step St2). The network packet generation unit 13 generates network packets by adding various predetermined headers (for example, RTP header, UDP / IP header) to the individual data packets acquired in step St2 (step St3). The network packet generation unit 13 writes the individual network packets generated in step St3 to the wireless buffer 21 (step St4).

[0074] If the network packet generation unit 13 succeeds in writing to the wireless buffer 21 in step St4 (step St5, YES), it performs the processing in step St10. On the other hand, if the network packet generation unit 13 fails to write to the wireless buffer 21 in step St4 (step St5, NO), it increments the write retry count N obtained in step St1 (step St6). If the write retry count N is less than the upper limit value TH_N obtained in step St1 (step St7, NO), the network packet generation unit 13 suspends writing the network packet to the wireless buffer 21 for a write waiting time TW obtained in step St1 and waits (step St8). After step St8, the processing of the network packet generation unit 13 returns to step St5.

[0075] On the other hand, if the network packet generation unit 13 determines that the number of write retries N has reached the upper limit value TH_N obtained in step St1 (step St7, YES), it increments the number of discarded packets Y due to timeout and sends the number of discarded packets Y to the video communication quality evaluation unit 14 (step St9). The network packet generation unit 13 calculates the total data amount D1 of network packets that were successfully written to the wireless buffer 21 per unit time and sends the calculation result of the total data amount D1 to the video communication quality evaluation unit 14 (step St10). For example, the network packet generation unit 13 may calculate the total data amount D1 by multiplying the "number of network packets written to the wireless buffer 21" by the "size of one network packet". With this, the processing of the network packet generation procedure by the network packet generation unit 13 is completed.

[0076] Figures 9 and 10 are flowcharts illustrating an example of a video communication quality evaluation procedure. The video communication quality evaluation procedure shown in Figures 9 and 10 is mainly performed periodically by the video communication quality evaluation unit 14.

[0077] In Figure 9, the video communication quality evaluation unit 14 reads and acquires various setting values ​​(step St11). These setting values ​​include, for example, the quality judgment threshold TH_Y based on the number of discarded packets and the quality judgment threshold TH_OK_W based on discarded packets and wireless bandwidth. The video communication quality evaluation unit 14 sets the current number of consecutive good wireless bandwidth counts, OK_W (step St12). The video communication quality evaluation unit 14 acquires the number of discarded packets Y due to timeout from the network packet generation unit 13 (step St13).

[0078] The video communication quality evaluation unit 14 acquires the current bandwidth setting value (bandwidth (W)) (step St14) and calculates the quality judgment threshold TH_W based on the wireless buffer write success bandwidth based on the acquired bandwidth (W) (step St15). Specifically, the video communication quality evaluation unit 14 calculates the quality judgment threshold TH_W based on the wireless buffer write success bandwidth by calculating bandwidth (W) / 2. For example, if the bandwidth (W) is 2 Mbps (see bandwidth (5)), the quality judgment threshold TH_W based on the wireless buffer write success bandwidth is calculated to be 1 Mbps.

[0079] The video communication quality evaluation unit 14 checks the time T1 when the previous video communication quality evaluation process was executed and the current time T2 (step St16), and obtains the calculation result of the total amount of network packets D1 that were successfully written to the wireless buffer 21 per unit time from the network packet generation unit 13 (step St17). Furthermore, the video communication quality evaluation unit 14 calculates the bandwidth W_CAL that was successfully written to the wireless buffer 21 per unit time (step St17). For example, the video communication quality evaluation unit 14 may calculate the bandwidth W_CAL that was successfully written to the wireless buffer 21 per unit time as the calculation result of "calculation result of the total amount of network packets D1 that were successfully written to the wireless buffer 21 per unit time" / (T2 - T1).

[0080] If the video communication quality evaluation unit 14 determines that the number of discarded packets Y obtained in step St13 is greater than the quality judgment threshold TH_Y obtained in step St11 (step St18, YES), it changes the current continuous wireless bandwidth good count OK_W set in step St12 to 0 (zero) (step St19). Following the processing in step St19, the video communication quality evaluation unit 14 generates a bandwidth change instruction to reduce the current bandwidth by one level and a size change instruction to reduce the current packet size by one level (step St20). After step St20, the processing of the video communication quality evaluation unit 14 proceeds to step St30.

[0081] On the other hand, if the video communication quality evaluation unit 14 determines that the number of discarded packets Y obtained in step St13 is less than or equal to the quality judgment threshold TH_Y based on the number of discarded packets obtained in step St11 (step St18, NO), it proceeds to the process in step St21. Specifically, the video communication quality evaluation unit 14 determines whether the bandwidth W_CAL of successful writes to the wireless buffer 21 per unit time, calculated in step St17, is greater than the quality judgment threshold TH_W based on the bandwidth of successful wireless buffer writes, calculated in step St15 (step St21). If it is determined that the bandwidth W_CAL of successful writes to the wireless buffer 21 per unit time is less than or equal to the quality judgment threshold TH_W based on the bandwidth of successful wireless buffer writes (step St21, NO), the video communication quality evaluation unit 14 proceeds to step St19. In other words, because it is difficult to successfully write network packets to the wireless buffer 21, the current bandwidth and packet size are deemed inappropriate and are changed to be reduced by one level each.

[0082] If the video communication quality evaluation unit 14 determines that the bandwidth W_CAL successfully written to the wireless buffer 21 per unit time is greater than the quality judgment threshold TH_W based on the bandwidth successfully written to the wireless buffer (step St21, YES), it proceeds to step St22. Specifically, the video communication quality evaluation unit 14 determines whether the bandwidth W_CAL successfully written to the wireless buffer 21 per unit time is greater than the quality judgment threshold TH_OK_W obtained in step St11 based on discarded packets and wireless bandwidth (step St22). If it determines that the bandwidth W_CAL successfully written to the wireless buffer 21 per unit time is less than the quality judgment threshold TH_OK_W based on discarded packets and wireless bandwidth (step St22, NO), the video communication quality evaluation unit 14 proceeds to step St25.

[0083] If the video communication quality evaluation unit 14 determines that the bandwidth W_CAL of successful writes to the wireless buffer 21 per unit of time is greater than the quality judgment threshold TH_OK_W based on discarded packets and wireless bandwidth (step St22, YES), it performs the processing in step St23. Specifically, the video communication quality evaluation unit 14 determines whether the current number of discarded packets Y is 0 (zero) or not (step St23). If the video communication quality evaluation unit 14 determines that the current number of discarded packets Y is 0 (zero) (step St23, YES), it increments the current number of consecutive good wireless bandwidth counts OK_W (step St24). After step St24, the processing of the video communication quality evaluation unit 14 proceeds to step St26.

[0084] If the video communication quality evaluation unit 14 determines that the current number of discarded packets Y is not 0 (no) (step St23, NO), it changes the current number of consecutive good wireless bandwidth counts OK_W to 0 (zero) (step St25). After step St25, the video communication quality evaluation unit 14 does not change the bandwidth or packet size and maintains them, and the video communication quality evaluation process by the video communication quality evaluation unit 14 ends. In this case, the video communication quality evaluation unit 14 may also generate a bandwidth maintenance instruction to maintain the current bandwidth setting and send it to the bandwidth control unit 15, and generate a size maintenance instruction to maintain the current packet size setting and send it to the packet size control unit 12.

[0085] If the video communication quality evaluation unit 14 determines that the current number of good continuous wireless bandwidth counts OK_W is equal to or greater than the quality judgment threshold TH_OK_W obtained in step St11 based on discarded packets and wireless bandwidth (step St26, YES), it generates a bandwidth change instruction to increase the current bandwidth by one level and a size change instruction to increase the current packet size by one level (step St27). After step St27, the processing of the video communication quality evaluation unit 14 proceeds to step St30. On the other hand, if it determines that the current number of good continuous wireless bandwidth counts OK_W is less than the quality judgment threshold TH_OK_W based on discarded packets and wireless bandwidth (step St26, NO), the video communication quality evaluation unit 14 does not change the bandwidth or packet size and maintains the current state, and the video communication quality evaluation processing by the video communication quality evaluation unit 14 ends.

[0086] In Figure 10, after step St20 or step St27, the video communication quality evaluation unit 14 generates an instruction to execute the bandwidth control processing procedure and sends it to the bandwidth control unit 15 (step St30), and then generates an instruction to execute the packet size processing procedure and sends it to the packet size control unit 12 (step St40). Details of the processing in steps St30 and St40 will be described later with reference to Figures 11 and 12, respectively. Although Figure 10 shows the bandwidth control processing procedure and the packet size processing procedure being executed in that order, the execution order of these two processing procedures is not limited to one order and may be executed in the reverse order.

[0087] After step St40, the video communication quality evaluation unit 14 initializes the number of discarded packets Y, which indicates the number of packets discarded due to timeout, to zero, and saves the current time T2 as the time T1 when this video communication quality evaluation process was executed (step St28). Furthermore, the video communication quality evaluation unit 14 initializes the total amount of network packets D1 that were successfully written to the wireless buffer 21 per unit time to zero (step St29). This completes the processing of the video communication quality evaluation procedure by the video communication quality evaluation unit 14.

[0088] Figure 11 is a flowchart showing an example of a bandwidth control processing procedure. The bandwidth control processing procedure shown in Figure 11 is periodically executed by the bandwidth control unit 15 based on instructions from the video communication quality evaluation unit 14.

[0089] In Figure 11, the bandwidth control unit 15 obtains various setting values ​​by referring to the correspondence table TBL1 shown in Figure 7, for example (step St31). These setting values ​​include, for example, the maximum bandwidth (bandwidth(6)) (i.e., 4Mbps) and the minimum bandwidth (bandwidth(1)) (i.e., 128kbps). The bandwidth control unit 15 obtains the current bandwidth setting value (bandwidth(W)) (step St32). The bandwidth control unit 15 determines whether the bandwidth change instruction obtained from the video communication quality evaluation unit 14 is a one-step reduction in bandwidth (step St33).

[0090] If the bandwidth control unit 15 determines that the bandwidth change instruction is a one-step reduction in bandwidth (step St33, YES), it determines whether the current bandwidth (W) obtained in step St32 is the minimum bandwidth (1) (step St34). If it determines that the current bandwidth (W) is the minimum bandwidth (1) (step St34, YES), the bandwidth control unit 15 maintains the current bandwidth (W), which is bandwidth (1), because it is not possible to further reduce the bandwidth from the minimum bandwidth (1). This completes the bandwidth control processing procedure by the bandwidth control unit 15.

[0091] If the bandwidth control unit 15 determines that the current bandwidth (W) is not the minimum bandwidth (1) (step St34, NO), it sets the bandwidth to decrease by one step (step St35). This completes the bandwidth control processing procedure by the bandwidth control unit 15.

[0092] If the bandwidth control unit 15 determines that the bandwidth change instruction is not a one-step decrease in bandwidth (step St33, NO), it determines whether the bandwidth change instruction obtained from the video communication quality evaluation unit 14 is an one-step increase in bandwidth (step St36). If it determines that the bandwidth change instruction is not an one-step increase in bandwidth (step St36, NO), the bandwidth control unit 15 maintains the current bandwidth (W). This completes the bandwidth control processing procedure by the bandwidth control unit 15.

[0093] If the bandwidth control unit 15 determines that the bandwidth change instruction is an increase of one level in bandwidth (step St36, YES), it determines whether the current bandwidth (W) obtained in step St32 is the maximum bandwidth (6) (step St37). If it is determined that the current bandwidth (W) is the maximum bandwidth (6) (step St37, YES), the bandwidth control unit 15 maintains the current bandwidth (W), which is bandwidth (6), because it is not possible to increase the bandwidth further from the maximum bandwidth (6). This completes the bandwidth control processing procedure by the bandwidth control unit 15.

[0094] If the bandwidth control unit 15 determines that the current bandwidth (W) is not the maximum bandwidth (6) (step St37, NO), it sets the bandwidth to increase the current bandwidth (W) by one step (step St38). This completes the bandwidth control processing procedure by the bandwidth control unit 15.

[0095] Figure 12 is a flowchart showing an example of a packet size processing procedure. The packet size processing procedure shown in Figure 12 is periodically executed by the packet size control unit 12 based on instructions from the video communication quality evaluation unit 14.

[0096] In Figure 12, the packet size control unit 12 obtains various setting values ​​by referring to the correspondence table TBL1 shown in Figure 7, for example (step St41). These setting values ​​include, for example, the maximum packet size, size (6) (i.e., 1.5 KB), and the minimum size, size (1) (i.e., 128 bytes). The packet size control unit 12 obtains the current packet size setting value (size (Z)) (step St42). The packet size control unit 12 determines whether the size change instruction obtained from the video communication quality evaluation unit 14 is a one-step decrease in size (step St43).

[0097] If the packet size control unit 12 determines that the size change instruction is to reduce the packet size by one step (step St43, YES), it determines whether the current size (Z) obtained in step St42 is the minimum packet size (1) (step St44). If it determines that the current size (Z) is the minimum packet size (1) (step St44, YES), the packet size control unit 12 maintains the current size (Z), which is size (1), because it is not possible to further reduce the packet size from the minimum packet size (1). This completes the packet size processing procedure by the packet size control unit 12.

[0098] If the packet size control unit 12 determines that the current size (Z) is not the minimum packet size (1) (step St44, NO), it sets the packet size to decrease the current size (Z) by one step (step St45). This completes the packet size processing procedure by the packet size control unit 12.

[0099] If the packet size control unit 12 determines that the size change instruction is not a decrease in packet size by one step (step St43, NO), it determines whether the size change instruction obtained from the video communication quality evaluation unit 14 is an increase in packet size by one step (step St46). If it determines that the size change instruction is not an increase in packet size by one step (step St46, NO), the packet size control unit 12 maintains the current size (Z). This completes the packet size processing procedure by the packet size control unit 12.

[0100] If the packet size control unit 12 determines that the size change instruction is to increase the packet size by one step (step St46, YES), it determines whether the current size (Z) obtained in step St42 is the maximum packet size (6) (step St47). If it determines that the current size (Z) is the maximum packet size (6) (step St47, YES), the bandwidth control unit 15 maintains the current size (Z), which is size (6), because the packet size cannot be increased further from the maximum packet size (6). This completes the packet size processing procedure by the packet size control unit 12.

[0101] If the packet size control unit 12 determines that the current size (Z) is not the maximum packet size (6) (step St47, NO), it sets the packet size to increase the current size (Z) by one step (step St48). This completes the packet size processing procedure by the packet size control unit 12.

[0102] Figures 13 and 14 show examples of correspondence tables for determining the communication rate index according to the number of wireless packet retransmissions. Figures 15 and 16 show examples of tables showing the relationship between the number of wireless packet retransmissions and the rate down value of the communication rate. The communication rates shown in Figures 13 and 14 (referred to only as "rate" in the figures) include, as an example, those corresponding to IEEE 802.11g, 11n, 11ac, and 11ax among the communication rates shown in Figure 6. The index shown in Figures 13 and 14 is the same as the index, which is the identification number of the communication rate shown in Figure 6.

[0103] The correspondence table TBL2 in Figure 13 and the correspondence table TBL3 in Figure 14 may be stored, for example, in the memory (not shown) of the wireless retransmission rate control unit 24. Both the correspondence table TBL2 and the correspondence table TBL3 are referenced by the wireless retransmission rate control unit 24 when determining the index of the communication rate when transmitting a wireless packet, according to the number of times the wireless packet has been retransmitted. In the correspondence table TBL2 in Figure 13, the maximum communication rate is 54 Mbps or MCS is 7 (see Figure 6), and the minimum communication rate is 1 Mbps (see Figure 6). On the other hand, in the correspondence table TBL3 in Figure 14, the maximum communication rate is 54 Mbps or MCS is 7 (see Figure 6), and the minimum communication rate is 6 Mbps or MCS is 0 (see Figure 6).

[0104] The correspondence table TBL2 in Figure 13 is referenced when the received field strength RSSI_VI of the received signal (e.g., the received response (Ack) of a wireless packet, measured by the wireless received field strength measurement unit 27, is less than the retransmission rate field strength threshold TH_RSSI_FB_Lim (see Figure 5). On the other hand, the correspondence table TBL3 in Figure 14 is referenced when the received field strength RSSI_VI of the received signal (e.g., the received response (Ack) of a wireless packet, measured by the wireless received field strength measurement unit 27, is greater than or equal to the retransmission rate field strength threshold TH_RSSI_FB_Lim (see Figure 5). Regardless of whether the wireless retransmission rate control unit 24 refers to the correspondence table TBL2 in Figure 13 or the correspondence table TBL3 in Figure 14, it determines the communication rate according to the number of wireless packet retransmissions according to the following common points.

[0105] In Figure 13, specifically, when the number of retransmissions of a wireless packet ranges from 1 to K (for example, K=8) (see range Phs1), the communication rate is discretely changed between the maximum and minimum communication rates. More specifically, when the number of retransmissions is "1", the index is "10", when the number of retransmissions is "2", the index is "5", when the number of retransmissions is "3", the index is "0", when the number of retransmissions is "4", the index is "10", when the number of retransmissions is "5", the index is "0", when the number of retransmissions is "6", the index is "10", when the number of retransmissions is "7", the index is "0", and when the number of retransmissions is "8", the index is "10". One possible reason for the period during which the receiver cannot receive an acknowledgment (Ack) of a wireless packet is the presence of electronic equipment (hereinafter sometimes referred to as "interfering equipment") emitting interfering radio waves to the camera 100. However, camera 100 cannot determine whether this interfering device is a microwave oven or another wireless LAN router. Therefore, the wireless retransmission rate control unit 24 operates on the principle that, in the initial range Phs1 where the number of retransmissions is small, it efficiently obtains opportunities to transmit wireless packets to the off-section where the interfering device is not emitting interfering radio waves, thereby suppressing interference in the transmission of wireless packets. This is achieved by alternately repeating transmission at a high communication rate (e.g., index "10") and transmission at a low communication rate (e.g., index "0"). Furthermore, by setting a high communication rate index, it is possible to perform wireless communication with a low probability of interference collision, while by setting a low communication rate index, it is possible to perform wireless communication with strong resistance to interference.

[0106] Furthermore, when the number of retransmissions of a wireless packet ranges from (K+1) (e.g., 9=8+1) to L (e.g., 18) (see range Phs2), the communication rate is changed to gradually decrease toward the minimum communication rate. More specifically, if the number of retransmissions is "9", the index is "9", if the number of retransmissions is "10", the index is "8", if the number of retransmissions is "11", the index is "7", if the number of retransmissions is "12", the index is "6", if the number of retransmissions is "13", the index is "5", if the number of retransmissions is "14", the index is "4", if the number of retransmissions is "15", the index is "3", if the number of retransmissions is "16", the index is "2", if the number of retransmissions is "17", the index is "1", and if the number of retransmissions is "18", the index is "0". The wireless retransmission rate control unit 24 is configured to decrease the communication rate by one step for each increase in the retransmission count in the intermediate range Phs2, thereby achieving a transmission with stronger interference resistance compared to the transmission in the initial range Phs1.

[0107] Furthermore, when the number of retransmissions of a wireless packet ranges from (L+1) (e.g., 19 = 18+1) to M (e.g., 32) (see range Phs3), the communication rate is fixed at the minimum communication rate. More specifically, the index is "0" regardless of whether the number of retransmissions is "19" or "32". In range Phs3, which is the final stage of retransmissions, the wireless retransmission rate control unit 24 fixes the communication rate to the minimum communication rate regardless of the number of retransmissions, thereby achieving more interference-resistant transmission compared to transmission in the intermediate stage range Phs2.

[0108] In Figure 14, specifically, when the number of retransmissions of a wireless packet ranges from 1 to K (for example, K=8) (see range Phs1), the communication rate is discretely changed between the maximum and minimum communication rates. More specifically, when the number of retransmissions is "1", the index is "10", when the number of retransmissions is "2", the index is "5", when the number of retransmissions is "3", when the number of retransmissions is "4", the index is "10", when the number of retransmissions is "5", the index is "3", when the number of retransmissions is "6", the index is "10", when the number of retransmissions is "7", the index is "3", and when the number of retransmissions is "8", the index is "10". One possible reason for the period during which the receiver cannot receive an acknowledgment (Ack) of a wireless packet is the presence of interference. However, camera 100 cannot determine whether this interference is a microwave oven or another wireless LAN router. Therefore, the wireless retransmission rate control unit 24 operates on the principle that, in the initial range Phs1a where the number of retransmissions is small, it efficiently obtains opportunities to transmit wireless packets to off-sections where no interfering equipment is emitting interfering radio waves, thereby suppressing interference in wireless packet transmission. This is achieved by alternately repeating transmission at a high communication rate (e.g., index "10") and transmission at a low communication rate (e.g., index "3"). Furthermore, by setting a high communication rate index, wireless communication with a low probability of interference collision can be performed, while by setting a low communication rate index, wireless communication with strong interference resistance can be performed.

[0109] Furthermore, when the number of retransmissions of a wireless packet is between (K+1) (e.g., 9=8+1) and L (e.g., 18) (see range Phs2a), the communication rate is changed to gradually decrease toward the minimum communication rate. More specifically, if the number of retransmissions is "9", the index is "9", if the number of retransmissions is "10", the index is "8", if the number of retransmissions is "11", the index is "7", if the number of retransmissions is "12", the index is "6", if the number of retransmissions is "13", the index is "5", if the number of retransmissions is "14", the index is "4", and if the number of retransmissions is "15", the index is "3". In range Phs2a, where the number of retransmissions is in the intermediate stage, the wireless retransmission rate control unit 24 is set to decrease the communication rate by one step for each increase in the number of retransmissions, thereby achieving transmission with stronger interference resistance compared to transmission in range Phs1a, which is in the initial stage.

[0110] Furthermore, when the number of retransmissions of a wireless packet ranges from (L+1) (e.g., 19 = 18+1) to M (e.g., 32) (see range Phs3a), the communication rate is fixed at the minimum communication rate. More specifically, the index is "3" regardless of whether the number of retransmissions is "19" to "32". In range Phs3a, where the number of retransmissions is in the final stage, the wireless retransmission rate control unit 24 fixes the communication rate to the minimum communication rate regardless of the number of retransmissions, thereby achieving more interference-resistant transmission compared to transmission in range Phs2a, which is in the intermediate stage.

[0111] The correspondence table TBL4 in Figure 15 schematically shows an example of the relationship between the number of retransmissions of a transmitted wireless packet T_RTY and the rate down value FB_DOWN(T_RTY) in the correspondence table TBL2 in Figure 13. The wireless retransmission rate control unit 24 determines the rate down value RF_DOWN(T_RTY) of the communication rate according to the number of retransmissions T_RTY by referring to the correspondence table TBL2 in Figure 13 or the correspondence table TBL4 in Figure 15.

[0112] The correspondence table TBL5 in Figure 16 schematically shows an example of the relationship between the number of retransmissions T_RTY of a transmitted wireless packet and the rate down value FB_DOWN(T_RTY) of the communication rate, extracted from the correspondence table TBL3 in Figure 14. The wireless retransmission rate control unit 24 determines the rate down value RF_DOWN(T_RTY) of the communication rate according to the number of retransmissions T_RTY by referring to the correspondence table TBL3 in Figure 14 or the correspondence table TBL5 in Figure 16.

[0113] Figures 17 and 18 are flowcharts illustrating an example of a retransmission rate processing procedure. The retransmission rate processing procedure shown in Figures 17 and 18 is executed by the wireless retransmission rate control unit 24 based on instructions from the wireless retransmission control unit 25.

[0114] In Figure 17, the wireless retransmission rate control unit 24 reads and acquires various thresholds (step St51). These thresholds include, for example, the retransmission rate field strength threshold TH_RSSI_FBLim and the maximum number of retransmissions TH_RTYMAX. The wireless retransmission rate control unit 24 sets the number of retransmissions T_RTY for the wireless packet being transmitted (step St52). To determine the minimum retransmission rate FB_MIN (i.e., the minimum communication rate), the wireless retransmission rate control unit 24 acquires the received field strength RSSI_VI of the received signal (e.g., the received response (Ack) of the wireless packet) from the wireless received field strength measurement unit 27 (step St53). The wireless retransmission rate control unit 24 determines whether the received field strength RSSI_VI of the received signal (e.g., the received response (Ack) of the wireless packet acquired in step St53 is greater than or equal to the retransmission rate field strength threshold TH_RSSI_FBLim acquired in step St51 (step St54).

[0115] If the wireless retransmission rate control unit 24 determines that the received field strength RSSI_VI of the received signal (e.g., the received response (Ack) of a wireless packet is less than the retransmission rate field strength threshold TH_RSSI_FBLim (step St54, NO), it refers to the correspondence table TBL2 in Figure 13 and determines and sets the minimum retransmission rate FB_MIN to 1 Mbps (step St55). On the other hand, if the wireless retransmission rate control unit 24 determines that the received field strength RSSI_VI of the received signal (e.g., the received response (Ack) of a wireless packet is greater than or equal to the retransmission rate field strength threshold TH_RSSI_FBLim (step St54, YES), it refers to the correspondence table TBL3 in Figure 14 and determines and sets the minimum retransmission rate FB_MIN to 6 Mbps or MCS to 0 (zero) (step St56). After determining the minimum retransmission rate, the wireless retransmission rate control unit 24 increments the retransmission count T_RTY of the wireless packet being transmitted (step St57).

[0116] In Figure 18, the wireless retransmission rate control unit 24 determines whether the retransmission count T_RTY of the wireless packet being transmitted, after being incremented in step St57, has reached the maximum retransmission count TH_RTYMAX (32 in the example of the correspondence table TBL3 in Figure 13 or the correspondence table TBL4 in Figure 14) obtained in step St51 (step St58). If the wireless retransmission rate control unit 24 determines that the retransmission count T_RTY of the wireless packet being transmitted has reached the maximum retransmission count TH_RTYMAX (step St58, YES), it determines that the transmission of that wireless packet has failed and deletes the wireless packet (step St59). This completes the processing of the retransmission rate processing procedure by the wireless retransmission rate control unit 24.

[0117] If the wireless retransmission rate control unit 24 determines that the number of retransmissions T_RTY for the wireless packet being transmitted has not reached the maximum number of retransmissions TH_RTYMAX (step St58, NO), it obtains the initial setting number (INDEX(INIT)) for the communication rate to retransmit the wireless packet (step St60). The initial setting number (INDEX(INIT)) is "10", which is the index that defines the maximum communication rate, regardless of whether the correspondence table TBL2 in Figure 13 or the correspondence table TBL3 in Figure 14 is referenced. The wireless retransmission rate control unit 24 determines the rate down value FB_DOWN(T_RTY) corresponding to the current value of the number of retransmissions T_RTY for the wireless packet being transmitted by referring to either the correspondence table TBL4 in Figure 15 or the correspondence table TBL5 in Figure 16 (step St61).

[0118] The wireless retransmission rate control unit 24 calculates the next communication rate setting number for the wireless packet to be retransmitted (step St62) using the initial communication rate number (INDEX(INIT)) obtained in step St60 and the rate down value FB_DOWN(T_RTY) determined in step St61. For example, the wireless retransmission rate control unit 24 calculates the next communication rate setting number for the wireless packet to be retransmitted by subtracting the rate down value FB_DOWN(T_RTY) from the initial communication rate number (INDEX(INIT)).

[0119] The wireless retransmission rate control unit 24 determines whether the next communication rate setting number calculated in step St62 is equal to or greater than the minimum retransmission rate FB_MIN set in step St55 or step St56 (step St63). If it is determined that the next communication rate setting number is equal to or greater than the minimum retransmission rate FB_MIN (step St63, YES), the wireless retransmission rate control unit 24 retransmits the wireless packet using that minimum retransmission rate FB_MIN. This completes the processing of the retransmission rate processing procedure by the wireless retransmission rate control unit 24.

[0120] If the wireless retransmission rate control unit 24 determines that the next communication rate setting number is less than the minimum retransmission rate FB_MIN (step St63, NO), it rounds the next communication rate setting number to the minimum retransmission rate (step St64). In other words, the wireless retransmission rate control unit 24 sets the next communication rate setting number to the minimum retransmission rate FB_MIN in order to retransmit wireless packets based on the minimum retransmission rate FB_MIN. This completes the retransmission rate processing procedure by the wireless retransmission rate control unit 24.

[0121] Figure 19 is a diagram that shows a comparative example of the signal waveform of an interfering radio wave from a microwave oven and an example of the signal waveform of a wireless packet transmission signal from camera 100. The horizontal axis in Figure 19 represents time. The signal waveform PY1 in the upper part of Figure 19 shows the signal waveform of an interfering radio wave from a microwave oven as an example of an interfering device. The signal waveform PY2 in the lower part of Figure 19 shows the signal waveform of a wireless packet transmission signal from camera 100.

[0122] As explained with reference to Figure 2, the microwave oven has the characteristic of periodically emitting radio waves (interfering radio waves) in the same frequency band (e.g., 2.4 GHz band) as the camera 100. In the example in Figure 19, of the 8.33 ms period (see Figure 2) consisting of one on-period and one off-period of the microwave oven, 6 ms is the on-period and the remaining 2.33 ms is the off-period. More specifically, in the signal waveform PY1 of the interfering radio waves from the microwave oven, for example, from time t10 to time t11 is the off-period of one period (see Figure 2). Also, from time t11 to time t12 is the on-period of one period (see Figure 2), and from time t12 to time t13 is the off-period of the same one period.

[0123] For example, high-level signal characteristics AC1 and AC2 are observed in the off-intervals (e.g., times t10-t11, t12-t13), which correspond to the so-called wireless packet acknowledgment (Ack). In other words, wireless packets are delivered from camera 100 to the receiver during these off-intervals. This indicates that the transmission of wireless packets from camera 100 to the receiver was successful. This is also evident from the fact that high-level signal characteristics AC1a and AC2a are observed in the signal waveform PY2 of the wireless packet transmission signal from camera 100 during the same off-intervals (e.g., times t10-t11, t12-t13). However, these off-intervals are short, and during the longer on-intervals other than the off-intervals (e.g., times t11-t12), wireless packets are not delivered from camera 100 to the receiver. In other words, the transmission of wireless packets from camera 100 to the receiver failed. Thus, although it depends on the distance (in other words, the relative position) between the camera 100 and the microwave oven, if there is a microwave oven acting as an interference source between the camera 100, which uses the 2.4GHz band for Wi-Fi (registered trademark), and the receiver, the transmission of the desired wireless packet signal (for example, the video signal of the imaging area) will only be successful during short off-periods.

[0124] Therefore, the camera 100 according to this embodiment dynamically changes the packet size and bandwidth constituting the wireless packet based on fluctuations in wireless quality, even when placed in an environment where a microwave oven using the same frequency band ISM band is in operation, and further determines the communication rate of the wireless packet according to the number of times the wireless packet has been retransmitted. As a result, the camera 100 can efficiently transmit wireless packets to the receiver even during short off-periods when the microwave oven is not in operation.

[0125] Figures 20, 21, and 22 are diagrams that show, in comparison, an example of a signal waveform of interfering radio waves from a wireless LAN repeater and an example of a signal waveform of a wireless packet transmission signal from camera 100. The horizontal axis in each of Figures 20 to 22 represents time. The upper signal waveforms PY1a, PY1b, and PY1c in Figures 20 to 22 show the signal waveforms of interfering radio waves from another wireless LAN router as an example of an interfering device. The lower signal waveforms PY2a, PY2b, and PY2c in Figures 20 to 22 show the signal waveforms of a wireless packet transmission signal from camera 100.

[0126] As explained with reference to Figure 3, another wireless LAN router, as an example of a source of interference, has the characteristic of emitting radio waves (interference signals) whose signal level fluctuates irregularly over time. In the example in Figure 20, in the signal waveform PY1a of the interference signal from another wireless LAN router, for example, the time from time t14 to time t15 (0.3 ms) is an off-interval (see Figure 2), and a signal characteristic AC3 with a high signal level is observed during this time, which corresponds to the so-called wireless packet reception response (Ack). In other words, during this off-interval, a wireless packet is delivered from camera 100 to the receiver. That is, the transmission of wireless packets from camera 100 to the receiver is successful. However, these off-intervals are short in duration, and during the longer on-intervals other than the off-intervals, wireless packets are not delivered from camera 100 to the receiver. That is, the transmission of wireless packets from camera 100 to the receiver fails. Thus, although it also depends on the distance (in other words, the relative position) between the camera 100 and other wireless LAN routers, if there is another wireless LAN router that acts as an interference source between the camera 100, which uses the 2.4GHz band for Wi-Fi (registered trademark), and the receiver, the transmission of the desired wireless packet signal (for example, the video signal of the imaging area) will only be successful during short off-periods.

[0127] Therefore, the camera 100 according to this embodiment dynamically changes the packet size and bandwidth constituting the wireless packet based on fluctuations in wireless quality, even when placed in an environment where other wireless LAN routers using the same 2.4GHz frequency band are operating, and further determines the communication rate of the wireless packet according to the number of retransmissions of the wireless packet. For example, in the initial range Phs1 where the number of wireless packet retransmissions is not large, the camera 100 sets a high communication rate for the wireless packet (Figures 13 and 14). As a result, the camera 100 can efficiently transmit wireless packets to the receiver even during short off-periods when other wireless LAN routers are not operating.

[0128] Furthermore, in the example shown in Figure 21, in the signal waveform PY1b of the interfering radio waves from another wireless LAN router, for example, the time from time t16 to time t17 is an off-interval (see Figure 2), and a signal characteristic AC4 with a high signal level is observed during this time, which corresponds to the so-called wireless packet reception response (Ack). In other words, during this off-interval, wireless packets are delivered from camera 100 to the receiver. That is, the transmission of wireless packets from camera 100 to the receiver is successful. However, these off-intervals are short, and during the longer on-intervals other than the off-intervals, wireless packets are not delivered from camera 100 to the receiver. That is, the transmission of wireless packets from camera 100 to the receiver fails. Thus, although it also depends on the distance (in other words, the relative position) between camera 100 and other wireless LAN routers, if there is another wireless LAN router that acts as an interference source between camera 100, which uses the 2.4GHz band for Wi-Fi (registered trademark), and the receiver, the transmission of the desired wireless packet signal (e.g., video signal of the imaging area) will only be successful during short off-intervals.

[0129] Therefore, the camera 100 according to this embodiment dynamically changes the packet size and bandwidth constituting the wireless packet based on fluctuations in wireless quality, even when placed in an environment where other wireless LAN routers using the same 2.4GHz frequency band are operating, and further determines the communication rate of the wireless packet according to the number of retransmissions of the wireless packet. For example, in the intermediate stage range Phs2 where the number of wireless packet retransmissions has increased, the camera 100 is set to gradually decrease the communication rate of the wireless packet one step at a time (Figures 13 and 14). As a result, the camera 100 can efficiently and stably transmit wireless packets to the receiver even during off-periods that are longer than the signal waveform PY1a in Figure 20.

[0130] Furthermore, in the example shown in Figure 22, the signal waveform PY1c of the interfering radio waves from another wireless LAN router shows that, for example, the time from time t20 to time t21 and the time from time t22 to time t23 are both off-periods (see Figure 2). High signal level characteristics AC5 and AC6 are observed during these times, which correspond to the so-called wireless packet reception acknowledgment (Ack). In other words, during these off-periods, wireless packets are delivered from camera 100 to the receiver. That is, the transmission of wireless packets from camera 100 to the receiver is successful. However, these off-periods are short, and during the longer on-periods other than the off-periods, wireless packets are not delivered from camera 100 to the receiver. That is, the transmission of wireless packets from camera 100 to the receiver fails. Thus, although it also depends on the distance (in other words, the relative position) between the camera 100 and other wireless LAN routers, if there is another wireless LAN router that acts as an interference source between the camera 100, which uses the 2.4GHz band for Wi-Fi (registered trademark), and the receiver, the transmission of the desired wireless packet signal (for example, the video signal of the imaging area) will only be successful during short off-periods.

[0131] Therefore, the camera 100 according to this embodiment dynamically changes the packet size and bandwidth constituting the wireless packet based on fluctuations in wireless quality, even when placed in an environment where other wireless LAN routers using the same 2.4GHz frequency band are operating, and further determines the communication rate of the wireless packet according to the number of retransmissions of the wireless packet. For example, in the final stage range Phs3, where the number of wireless packet retransmissions is high, the camera 100 is set to fix the communication rate of the wireless packet to the minimum communication rate (Figures 13 and 14). As a result, the camera 100 can efficiently and stably transmit wireless packets to the receiver even during off-periods that are longer than the signal waveform PY1b in Figure 21.

[0132] As described above, the wireless transmitting device (e.g., camera 100) according to this embodiment comprises an application unit 1 that acquires a plurality of network packets constituting image data of an imaging area, a wireless unit 2 that generates wireless packets for wireless transmission from each of the plurality of network packets, and a transmitting unit (e.g., transceiver unit 3) that transmits wireless packets to a receiver (e.g., intercom master unit IPM 1) via an antenna 33. The wireless unit 2 has at least a wireless retransmission rate control unit 24 that determines a communication rate for retransmitting wireless packets based on the strength of the received signal from the receiver (e.g., the received electric field strength RSSI_VI of the received response (Ack) of the wireless packet). The transmitting unit retransmits wireless packets using the communication rate determined by the wireless retransmission rate control unit 24. As a result, the wireless transmitting device (e.g., camera 100) can flexibly set the communication rate of wireless packets in accordance with fluctuations in wireless quality, even when there are signal sources in the vicinity other than itself (i.e., camera 100) that emit wireless signals in the same frequency band that cause interference to wireless communication. Therefore, a wireless transmitter (e.g., camera 100) can perform wireless communication with a low probability of interference and collision by setting a high communication rate, while simultaneously performing wireless communication with high interference resistance by setting a low communication rate, thereby effectively suppressing the occurrence of interference in wireless signals.

[0133] Furthermore, if the strength of the received signal from the receiver (e.g., intercom master unit IPM1) (e.g., the received field strength RSSI_VI of the received response (Ack) of the wireless packet) is less than the retransmission rate threshold (e.g., the retransmission rate field strength threshold TH_RSSI_FBLim), the wireless retransmission rate control unit 24 selects a second correspondence table (e.g., correspondence table TBL2 in Figure 13) that defines the relationship between the communication rate, including the minimum retransmission rate for transmitting the wireless packet, and the number of times the wireless packet should be retransmitted. Based on the selected second correspondence table, the wireless retransmission rate control unit 24 determines the communication rate for transmitting the wireless packet. This allows the wireless transmitter (e.g., camera 100) to adaptively determine what communication rate to use when the communication quality between the camera 100 and the receiver is poor to the extent that the strength of the received signal from the receiver (e.g., intercom master unit IPM1) is less than the retransmission rate field strength threshold TH_RSSI_FBLim.

[0134] Furthermore, the second correspondence table (for example, the correspondence table TBL2 in Figure 13) defines the relationship between the communication rate and the number of retransmissions of a wireless packet. This means that for retransmissions from 1 to K (K: a default integer greater than or equal to 2, e.g., 8), the communication rate is discretely changed between the maximum and minimum communication rates and between the minimum and maximum communication rates. For retransmissions from (K+1) to L (L: a default integer greater than or equal to (K+2), e.g., 18), the communication rate is gradually decreased from the maximum communication rate. For retransmissions from (L+1) to M (M: a default integer greater than or equal to (L+2), e.g., 32), the communication rate is fixed and maintained at the minimum communication rate. As a result, the wireless transmitter (e.g., camera 100) divides the number of retransmissions of the wireless packet transmission signal into three stages (specifically, the initial stage range Phs1, the intermediate stage range Phs2, and the final stage range Phs3), and determines the communication rate differently for each stage. Therefore, a wireless transmitter (e.g., camera 100) can increase the probability of transmitting wireless packets by using different methods depending on the number of retransmissions: setting a high communication rate and transmitting in a short time; setting a low communication rate and transmitting for a longer time but with stronger interference resistance; gradually lowering the communication rate by one step each time the number of retransmissions increases; and fixing the communication rate to the minimum communication rate and transmitting when the number of retransmissions exceeds a certain value.

[0135] Furthermore, the second correspondence table (for example, the correspondence table TBL2 in Figure 13) defines the relationship between the communication rate and the number of retransmissions of wireless packets, stating that from 1 to K (for example, 8) the communication rate alternates between the maximum communication rate and the minimum communication rate. This allows the wireless transmitter (for example, camera 100) to efficiently obtain opportunities to transmit wireless packets into off-sections where no interfering devices are emitting interfering radio waves by alternately transmitting at a high communication rate (for example, index "10") and a low communication rate (for example, index "0") in the initial range Phs1 where the number of retransmissions is low, thereby suppressing interference in wireless packet transmission.

[0136] Furthermore, if the strength of the received signal from the receiver (e.g., intercom master unit IPM1) (e.g., the received field strength RSSI_VI of the received response (Ack) of the wireless packet) is greater than the retransmission rate threshold (e.g., the retransmission rate field strength threshold TH_RSSI_FBLim), the wireless retransmission rate control unit 24 selects a third correspondence table (e.g., correspondence table TBL3 in Figure 14) that defines the relationship between the communication rate, including the minimum retransmission rate for transmitting the wireless packet, and the number of times the wireless packet should be retransmitted. Based on the selected third correspondence table, the wireless retransmission rate control unit 24 determines the communication rate for transmitting the wireless packet. This allows the wireless transmitter (e.g., camera 100) to adaptively determine what communication rate to use to transmit the wireless packet signal, provided that the communication quality between the camera 100 and the receiver is not so poor that the strength of the received signal from the receiver (e.g., intercom master unit IPM1) is greater than the retransmission rate field strength threshold TH_RSSI_FBLim.

[0137] Furthermore, the third correspondence table (for example, the correspondence table TBL3 in Figure 14) defines the relationship between the communication rate and the number of retransmissions of wireless packets. For retransmissions from 1 to K (K: a default value that is an integer of 2 or greater, e.g., 8), the communication rate is discretely changed between the maximum communication rate and the minimum communication rate, and between the minimum communication rate and the maximum communication rate. For retransmissions from (K+1) to L (L: a default value that is an integer of (K+2) or greater, e.g., 18), the communication rate is changed to gradually decrease from the maximum communication rate. For retransmissions from (L+1) to M (M: a default value that is an integer of (L+2) or greater, e.g., 32), the communication rate is fixed and maintained at the minimum communication rate. As a result, the wireless transmitter (e.g., camera 100) divides the number of retransmissions of the wireless packet transmission signal into three stages (specifically, the initial stage range Phs1, the intermediate stage range Phs2, and the final stage range Phs3), and determines the communication rate differently for each stage, although the minimum communication rate when wireless quality is good is different from the minimum communication rate when wireless quality is poor. Therefore, the wireless transmitter (e.g., camera 100) can increase the probability of transmitting wireless packets by using different methods depending on the number of retransmissions: an attempt to transmit in a short time with a high communication rate, an attempt to transmit with a low communication rate which takes longer but has stronger interference resistance, an attempt to gradually lower the communication rate by one stage each time the number of retransmissions increases, and an attempt to fix the communication rate at the minimum communication rate when the number of retransmissions exceeds a certain value.

[0138] Furthermore, the third correspondence table (for example, correspondence table TBL3 in Figure 14) defines the relationship between the communication rate and the number of retransmissions of wireless packets, stating that from 1 to K (for example, 8) the communication rate alternates between the maximum communication rate and the minimum communication rate. This allows the wireless transmitter (for example, camera 100) to efficiently obtain opportunities to transmit wireless packets to off-sections where no interfering devices are emitting interfering radio waves by alternately transmitting at a high communication rate (for example, index "10") and a low communication rate (for example, index "3") in the initial range Phs1 where the number of retransmissions is low, thereby suppressing interference in wireless packet transmission.

[0139] Furthermore, the application unit 1 includes at least a bandwidth control unit 15 that variably controls the bandwidth of network packets based on fluctuations in wireless quality between the receiver and the application unit, and a packet size control unit 12 that variably controls the size of network packets based on fluctuations in wireless quality. As a result, the wireless transmitter (e.g., camera 100) can flexibly set the packet bandwidth and packet size in accordance with fluctuations in wireless quality, thereby effectively suppressing interference of wireless signals.

[0140] Furthermore, the application unit 1 also includes a size-bandwidth evaluation unit (e.g., a video communication quality evaluation unit 14) that determines the amount of change for both size and bandwidth in conjunction with the wireless quality fluctuations. The size-bandwidth evaluation unit sends a size change instruction, including the determined amount of size change, to the packet size control unit 12, and a bandwidth change instruction, including the determined amount of bandwidth change, to the bandwidth control unit 15. If the wireless environment between the camera 100 and the receiver is poor, it is desirable to shorten the packet transmission time, so reducing the packet size is a possibility. However, if only the packet size is reduced while maintaining the bandwidth, the overhead in packet division will increase, and the update of image data is likely to be slower. Therefore, the wireless transmitter (e.g., the camera 100) can adaptively generate packets in response to fluctuations in wireless quality by changing both the packet size and bandwidth in conjunction, thereby suppressing the occurrence of communication overhead.

[0141] Furthermore, the size-bandwidth evaluation unit (e.g., video communication quality evaluation unit 14) maintains a first correspondence table (e.g., correspondence table TBL1 in Figure 7) that defines the relationship between size and bandwidth in response to fluctuations in wireless quality. Based on the first correspondence table, the size-bandwidth evaluation unit determines the respective changes in size and bandwidth. As a result, even when fluctuations in wireless quality occur, the wireless transmitter (e.g., camera 100) can adaptively determine and set the packet size and bandwidth relative to the current packet size and bandwidth settings.

[0142] Furthermore, the application unit 1 further includes a camera unit 11 that generates image data of the imaging area. This allows the wireless transmission device (e.g., camera 100) to transmit the image data obtained by capturing the imaging area to a receiver (e.g., intercom master unit IPM1) using the 2.4GHz band of Wi-Fi®.

[0143] Although various embodiments have been described above with reference to the attached drawings, this disclosure is not limited to such examples. It will be clear to those skilled in the art that various modifications, alterations, substitutions, additions, deletions, and equivalents can be conceived within the scope of the claims, and these will also be understood to fall within the technical scope of this disclosure. Furthermore, the components of the various embodiments described above can be combined arbitrarily without departing from the spirit of the invention. [Industrial applicability]

[0144] This disclosure is useful as a wireless transmitting device and wireless transmitting method for suppressing the occurrence of wireless signal interference even when there is a signal source other than the device itself that transmits wireless signals in the same frequency band that cause interference. [Explanation of Symbols]

[0145] 1. Application Section 2. Wireless Section 3. Transmitter / Receiver Unit 11 Camera Section 12 Packet Size Control Unit 13 Network Packet Generation Unit 14. Video Communication Quality Evaluation Department 15 Bandwidth Control Unit 21 Wireless Buffer 22 Wireless packet generation unit 23 Wireless Transmission Control Unit 24 Wireless retransmission rate control unit 25 Wireless retransmission control unit 26 Wireless Receiving Control Unit 27 Wireless Received Field Strength Measurement Unit 28 Wireless Communication Quality Evaluation Department 31 RF section 32 Amplifier section 33 Antennas 100 Cameras

Claims

1. An application unit that acquires multiple network packets that constitute the image data of the imaging area, A wireless unit that generates wireless packets for wireless transmission from each of the aforementioned plurality of network packets, The system includes a transmitting unit that transmits the wireless packets to a receiver via an antenna, The aforementioned wireless unit is The system includes at least a wireless retransmission rate control unit that determines a communication rate for retransmitting the wireless packet based on the strength of the signal received from the receiver, The aforementioned transmitting unit The wireless packet is retransmitted using the communication rate determined by the wireless retransmission rate control unit. The wireless retransmission rate control unit, If the strength of the received signal from the receiver is less than the retransmission rate threshold, a second correspondence table is selected that defines the relationship between the communication rate, including the minimum retransmission rate for transmitting the wireless packet, and the number of retransmissions of the wireless packet. Based on the selected second correspondence table, the communication rate for transmitting the wireless packet is determined. The aforementioned second correspondence table is, The communication rate is discretely changed between the maximum communication rate and the minimum communication rate and between the minimum communication rate and the maximum communication rate, from 1 to K (K: a default value which is an integer of 2 or more) for the number of retransmissions. The communication rate is changed to be gradually reduced toward the minimum communication rate from (K+1) to L (L: a default value which is an integer greater than or equal to (K+2)) when the number of retransmissions is (K+1). The communication rate is fixed and maintained at the minimum communication rate until the number of retransmissions is from (L+1) to M (M: a default value which is an integer greater than or equal to (L+2)). This defines the relationship between the communication rate and the number of retransmissions of the wireless packet. Wireless transmitter.

2. The aforementioned second correspondence table is, For the number of retransmissions from 1 to K, the communication rate is alternately repeated in the order of the maximum communication rate and the minimum communication rate. This defines the relationship between the communication rate and the number of retransmissions of the wireless packet. The wireless transmitting device according to claim 1.

3. An application unit that acquires multiple network packets constituting image data of an imaging area, A wireless unit that generates wireless packets for wireless transmission from each of the aforementioned plurality of network packets, The system includes a transmitting unit that transmits the wireless packets to a receiver via an antenna, The aforementioned wireless unit is The system includes at least a wireless retransmission rate control unit that determines a communication rate for retransmitting the wireless packet based on the strength of the signal received from the receiver, The aforementioned transmitting unit The wireless packet is retransmitted using the communication rate determined by the wireless retransmission rate control unit. The wireless retransmission rate control unit, If the strength of the received signal from the receiver is greater than the retransmission rate threshold, a third correspondence table is selected that defines the relationship between the communication rate, which includes the minimum retransmission rate for transmitting the wireless packet, and the number of retransmissions of the wireless packet. Based on the selected third correspondence table, the communication rate for transmitting the wireless packet is determined. Wireless transmitter.

4. The third correspondence table is: The communication rate is discretely changed between the maximum communication rate and the minimum communication rate and between the minimum communication rate and the maximum communication rate, from 1 to K (K: a default value which is an integer of 2 or more) for the number of retransmissions. The communication rate is changed to be gradually reduced toward the minimum communication rate from (K+1) to L (L: a default value which is an integer greater than or equal to (K+2)) when the number of retransmissions is (K+1). The communication rate is fixed and maintained at the minimum communication rate until the number of retransmissions is from (L+1) to M (M: a default value which is an integer greater than or equal to (L+2)). This defines the relationship between the communication rate and the number of retransmissions of the wireless packet. The wireless transmitting device according to claim 3.

5. The third correspondence table is: For the number of retransmissions from 1 to K, the communication rate is alternately repeated in the order of the maximum communication rate and the minimum communication rate. This defines the relationship between the communication rate and the number of retransmissions of the wireless packet. The wireless transmitting device according to claim 4.

6. The aforementioned application unit is A bandwidth control unit that variably controls the bandwidth of the network packets based on fluctuations in wireless quality between the receiver and the network, The system includes at least a packet size control unit that variably controls the size of the network packets based on the fluctuations in the wireless quality, The wireless transmitting device according to claim 1.

7. The application unit is A bandwidth control unit that variably controls the bandwidth of the network packets based on fluctuations in wireless quality between the receiver and the network, The system includes at least a packet size control unit that variably controls the size of the network packets based on the fluctuations in the wireless quality, The wireless transmitting device according to claim 3.

8. The aforementioned application unit is The system further includes a size-bandwidth evaluation unit that determines the respective amounts of change so as to change both the size and the bandwidth in conjunction with each other based on the fluctuations in the wireless quality, The size-bandwidth evaluation unit sends a size change instruction to the packet size control unit, including the determined amount of change in size, and sends a bandwidth change instruction to the bandwidth control unit, including the determined amount of change in bandwidth. The wireless transmission device according to claim 6.

9. The application unit is The system further includes a size-bandwidth evaluation unit that determines the respective amounts of change so as to change both the size and the bandwidth in conjunction with each other based on the fluctuations in the wireless quality, The size-bandwidth evaluation unit sends a size change instruction to the packet size control unit, including the determined amount of change in size, and sends a bandwidth change instruction to the bandwidth control unit, including the determined amount of change in bandwidth. The wireless transmitting device according to claim 7.

10. The size-bandwidth evaluation unit maintains a first correspondence table that defines the relationship between the size and the bandwidth in response to fluctuations in the wireless quality, and determines the respective amounts of change to the size and the bandwidth based on the first correspondence table. The wireless transmitting device according to claim 8.

11. The size-bandwidth evaluation unit maintains a first correspondence table that defines the relationship between the size and the bandwidth in accordance with the fluctuation of the wireless quality, and determines the respective amounts of change to the size and the bandwidth based on the first correspondence table. The wireless transmitting device according to claim 9.

12. The aforementioned application unit is The system further includes a camera unit that generates image data of the aforementioned imaging area, The wireless transmitting device according to claim 1.

13. The application unit is The system further includes a camera unit that generates image data of the aforementioned imaging area, The wireless transmitting device according to claim 3.

14. The steps include acquiring multiple network packets that constitute the image data of the imaging area, The steps include generating a wireless packet for wireless transmission from each of the aforementioned plurality of network packets, The process includes the step of transmitting the wireless packet to a receiver via an antenna, The step of generating the aforementioned wireless packet is: The method further includes the step of determining a communication rate for retransmitting the wireless packet based on the strength of the signal received from the receiver, The step of transmitting the aforementioned wireless packet is: The method further includes the step of retransmitting the wireless packet using the determined communication rate, The step of generating the aforementioned wireless packet is: The system further includes the step of selecting a second correspondence table that defines the relationship between a communication rate including the minimum retransmission rate for transmitting the wireless packet and the number of retransmissions of the wireless packet, if the strength of the received signal from the receiver is less than a retransmission rate threshold, and determining the communication rate for transmitting the wireless packet based on the selected second correspondence table. The aforementioned second correspondence table is, The communication rate is discretely changed between the maximum communication rate and the minimum communication rate and between the minimum communication rate and the maximum communication rate, from 1 to K (K: a default value which is an integer of 2 or more) for the number of retransmissions. The communication rate is changed to be gradually reduced toward the minimum communication rate from (K+1) to L (L: a default value which is an integer greater than or equal to (K+2)) when the number of retransmissions is (K+1). The communication rate is fixed and maintained at the minimum communication rate until the number of retransmissions is from (L+1) to M (M: a default value which is an integer greater than or equal to (L+2)). This defines the relationship between the communication rate and the number of retransmissions of the wireless packet. Wireless transmission method.

15. A step of acquiring a plurality of network packets that constitute image data of an imaging area, The steps include generating a wireless packet for wireless transmission from each of the aforementioned plurality of network packets, The process includes the step of transmitting the wireless packet to a receiver via an antenna, The step of generating the aforementioned wireless packet is: The method further includes the step of determining a communication rate for retransmitting the wireless packet based on the strength of the signal received from the receiver, The step of transmitting the aforementioned wireless packet is: The method further includes the step of retransmitting the wireless packet using the determined communication rate, The step of generating the aforementioned wireless packet is: The system further comprises the step of selecting a third correspondence table that defines the relationship between a communication rate including the minimum retransmission rate for transmitting the wireless packet and the number of retransmissions of the wireless packet, if the strength of the received signal from the receiver is greater than a retransmission rate threshold, and determining the communication rate for transmitting the wireless packet based on the selected third correspondence table. Wireless transmission method.

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